Slot Car Speed Calculator

Slot car speed comes down to how fast the motor spins, how much that speed gets reduced by the gearing between the motor and the axle, and how far the drive tires travel per rotation. Motor RPM is the raw rotational speed of the motor itself; Gear Ratio is how many times the motor spins for one rotation of the axle (a 3:1 ratio means the motor turns three times for every one turn of the wheels), so a higher Gear Ratio slows the wheels down for a given Motor RPM in exchange for more torque, exactly like a lower gear in a car. Tire Diameter sets how far the car travels per wheel rotation -- a larger tire covers more ground per turn, the same way a bigger bicycle wheel covers more distance per pedal stroke. Actual Speed (mph) is the car's real, full-scale ground speed once Motor RPM is reduced by Gear Ratio and converted through Tire Diameter into a linear speed.

Tire Surface Speed (mph) reports the same physical quantity -- the linear speed of the tire's contact patch on the track -- so for a tire that isn't slipping, it reads the same as Actual Speed to the digit; it's included separately because racers sometimes reason about drivetrain performance in terms of tire surface speed specifically, independent of how that speed translates to a given track. Scale Speed (mph) answers a different question: what speed would this car be going if it were scaled up to a real, full-size vehicle at the selected Scale (HO's 1:87, 1:32, or 1:24) -- it multiplies Actual Speed by the scale factor, which is why even a modest slot car speed translates into a startling scale speed once blown up to real-world size. Laps/Min assumes a standard 30-foot track length to convert the car's linear speed into a lap rate for comparing setups on a common course.